1. Field of the Invention
This invention relates to a centrifugal oil pressure control device, and more particularly to a centrifugal oil pressure control device for a continuously variable transmission which includes a centrifugal oil pressure correction chamber so as to prevent centrifugal oil pressure from acting on the sheaves.
2. Description of the Related Art
A V-belt type continuously variable transmission which is used in an automotive vehicle is well known. This conventional device includes a V-belt, an input sheave, an output sheave and an oil pressure chamber. The oil pressure chamber is provided with each sheave, and oil pressure is supplied thereto or released therefrom. The V-belt is rotatably arranged between the input sheave and the output sheave, and the radius of the V-belt is varied to become a certain value by means of controlling oil pressure of the oil pressure chamber. As a result, shift changes are carried out in a continuously variable step.
In this case, the oil pressure chamber is rotated together with the sheave. Therefore, a centrifugal oil pressure occurs in the oil pressure chamber. The centrifugal oil pressure radially acts on the sheave and is outwardly, increased, so that the depression or movement of the sheave corresponds to an oil pressure of the oil pressure chamber. Thus, a desired shift change can not be exactly carried out. In order to avoid this problem, various types of devices having a centrifugal oil pressure correction chamber are proposed. For instance, Japanese Laid Open Patent Publications No. 59-99157 and 60-164068 are such examples.
In Japanese Laid Open Patent Publication No. 59-99157, as shown in FIG. 4, an oil pressure chamber 2 is provided with a movable sheave 1b. Moreover, a centrifugal oil pressure correction chamber 3 is provided at the opposite side of the oil pressure chamber 2 with respect to the movable sheave 1b and is filled with oil. Therefore, a centrifugal oil pressure is provided in the centrifugal oil pressure correction chamber 3 and acts in an opposite direction of depression or movement of the movable sheave 1b. As a result, the centrifugal oil pressure acting on the movable sheave 1b is decreased.
On the other hand, Japanese Laid Open Patent Publication No. 60-164068, in as shown in FIG. 5, an oil pressure correction chamber 13 is provided at the opposite side of an oil pressure chamber 12 with respect to a movable sheave 11b so as to avoid the same problem.
However, in reference to FIG. 4, a cylinder 4 of the oil pressure chamber 2 is axially extended and is movably provided on a piston 5. The centrifugal oil pressure chamber 3 is defined by the cylinder 4 and the piston 5. Therefore, the radial oil pressure area of the centrifugal oil pressure correction chamber 3 is smaller than that of the movable sheave 1b. Thereby, the remaining centrifugal oil pressure acts on the movable sheave 1b, so that a desired shift change can not be exactly carried out.
Also, in reference to FIG. 5, a cylinder 14 of the oil pressure chamber 12 is axially extended to a shaft 16 and is slidably movable on the shaft 16. The centrifugal oil pressure chamber 13 is defined by the cylinder 14 and a piston 15 which is disposed in the cylinder 14. Therefore, the radial oil pressure area of the centrifugal oil pressure correction chamber 13 is equal to that of the oil pressure chamber 12. As a result, the centrifugal oil pressure acting on the movable sheave 11b almost becomes naught. However, the axial movement of the cylinder 14 is required. Thus, a large axial space is required.